Annular knife sharpener



1959 c. H. M FARLAND 2,900,768

ANNULAR KNIFE SHARPENER Filed Sept. 22, 1958 mm. mm. M 3W. H B

ATTORNEYS United States Patent 6 ANNULAR KNIFE SHARPENER Charles H. MacFarland, Rocky River, Ohio, assignor to The Scott & Fetzer Company, Cleveland, Ohio, a corporation of Ohio Application September 22, 1958, Serial No. 762,644

Claims. (Cl. 51-197) This invention relates to a knife sharpener and particularly to a sharpener of the annular type which is mounted on a power shaft for rotation thereby. More particularly, the invention relates to the type of rotary sharpener in which an annular guide groove is provided for receiving the cutting edge of the knife to be sharpened, the groove being defined by abrasive material and serving both to abrade and to guide or position the knife blade.

A general object of the invention is to provide an annular guide groove type sharpener of improved design. The invention contemplates a guide groove which conforms itself to the shape of the knife blade being sharpened. The invention particularly embodies the concept of limiting the enlargement of the guide groove while simul taneously maintaining the blade conforming action so that the occurrence-of sharpening action is limited to the vicinity of the periphery of the annular sharpener to achieve a superior sharpening action. The organization is such that the guide groove cannot spread unduly but neverthelessthe guide groove readily conforms to the blade shape.

- The structure by which the new sharpening action is achieved includes flexible abrasive webs which are supported by backing members and are held in operative association with each other but which may be readily disassociated from their supports and from each other for replacement.

A particular advantage of the present invention is that the abrasive webs which are employed may comprise merelyflat abrasive discs of conventional shape rather than the special shapes (such as flanged discs or the like) which are necessary when the abrasive web is not supported.

. These and other objects and advantages of the invention will become more apparent from the following description of one concrete example of the invention.

a In the drawings, Figure 1 shows a side elevation of the example of the invention to be described in detail below. Figure 2 is a cross-section, taken on the plane of line 22 in Figure l.

.A pair of annular elastomeric members and 11 are provided. The members 10 and 11 are mounted coaxially on a drive shaft 12. In the illustrated example, a shoulder 13 is defined on the drive shaft 12 by means of a collar 14. Each of the members 10 and 11 has a front face in apposition to the other of the members. Thus, the member 10 has a front face 15 and the member 11 has a front face 16. The front faces 15 and 16 curve symmetrically relatively away from each other through a zone extending from radially intermediate locations to locations near the peripheries of the members 10 and 11. At points radially inside such zone, the front faces are spaced from each other a given and substantially con stant distance, which is equal to the combined thicknesses of the two abrasive webs associated with the members 10 and 11 and to be described below.

The pair of flexible, abrasive webs is illustrated in the drawings with the reference numerals 20 and 21. The

disc of paper or other material may be employed if desired. The flexible abrasive webs 20 and 21 are clamped between the elastomeric members 10 and 11 and against each other at locations radially inwardly of the abovementioned zone.

Each of the members 10 and 11 has a rear face opposite to its front face 15 or 16, and a stiff washer is received against each of said rear faces. Thus, a stiff washer 24 is received against the rear face of the annular member 10 and a stiff washer 25 is received against the rear face of the annular member 11. The washers 24 and 25 extend radially outwardly from the shaft 12 but are located radially inwardly from the abovementioned zone or at least the majority thereof.

Clamping means are provided on the shaft for engaging the washers. In the illustrated example, the clamping means comprises the shoulder 13 and an opposed retaining means which is tightenable to a predetermined positively defined minimum axial distance along the shaft 12 from the shoulder 13. The retaining means comprises the bolt 27 which is received in the tapped end of the shaft 12 and which is tightenable against the end face of the in the annular groove defined'between the webs 20 and.

21 at the radially outer portions of the structure. The clamping action of the bolt 27 and the shoulder 13 against the washers 24 and 25 serves to maintain the flexible webs 20 and 21 in clamped position between the members 10 and 11.

In the particular embodiment illustrated, the back faces of the members 10 and 11 have annular grooves 30 and 31 formed therein, and they also have formed therein additional grooves 32 and 33, respectively. In some cases, other groove arrangements may be used or the grooves may be dispensed with altogether. It will be noted in the illustrated embodiment that the outer peripheries of the washers 24 and 25 are in supporting engagement with their respective members 10 and 11 at the faces 22 and 23, respectively.

Where high powers are supplied through the shaft 12, as when the sharpener is employed as an accessory or attachment in connection with a power tool or household appliance which has a relatively powerful motor which will not readily stall, a fairly closely controlled safety release action may be particularly important to the prevent'ion of grabbing of the knife blade in the annular groove of the sharpener or burning of the knife blade. For example in a sharpener of the illustrated type where the outside diameter of the illustrated assembly is about 2% inches, a release torque of about 1 inch-pound is desirable. Dimensional tolerances and other tolerances of the several parts, particularly the elastomeric members 10 and 11 and the abrasive webs 20 and 21, may not be practically sufficiently closely controlled in production to provide with any assurance for close control of release torque, and if the motor driving the shaft 12 cannot be readily stalled, excessive torques of several inch-pounds or more may be imposed when grabbing occurs. Such excessive torques may cause the instrument being sharpened to be pulled from the users hand or they may cause burning of the blade. For a closer control of release torque, the stiff washers 24- and 25 may be made of springy metal and may be stressed in axial compression between the inner sides of the shoulder 13 and bolt head 27 on the one hand and the shoulder or face portions 22 and 23 of the members and 11 against which the peripheries of the washers are engaged on the other hand. The center bores of the members 10 and 11 may have an equal or slightly greater inside diameter than the outside diameter of the shaft 12, so that there is no degree of interference fit between the members 10 and 11 and the shaft 12. The shoulders 28 and 29 may be molded to be located slightly inwardly axially from the shoulders 22 and 23 so that there is very little frictional engagement between the shoulders 22 and 23 and the washers 24 and 25, even when the bolt 27 is tightened into clamping position. The drawing appropriately illustrates this condition, slight axial compression of the elastomer at the shoulders 22 and 23 having allowed the washers 24 and 25 to just contact the shoulders 28 and 29. Accordingly, torque is transmitted from the shaft 12 to the members 10 and 11 substantially exclusively through the side faces of the members 14 and 27 to the members 24 and 25 respectively and thence through theinterfaces at the shoulders 22 and 23, respectively. The driving friction at the metal-to-rubber interfaces 22 and 23 is substantially higher than that at the side faces of the members 14 and 27, so that the latter governs release torque. If the stiff washers 24 and 25 are made of spring material, then through a given axial range of compression each washer will act as a spring and through such range the driving friction at the side faces of the members 14 and 27 will vary only as a straight line function of the spring constant of such springs. Thus if the spring has an operating range of say inch, then the driving friction at the faces of the members 14 and 27 Will vary only moderately throughout a range of spacing between these faces of as much as inch. The drawing appropraitely illustrates suitable spring washers 24 and 25 in assembled condition, the center portions of the washers having been slightly bulged axially outwardly prior to assembly of the sharpener. The washers may be replaced by other equivalent backing members comprising stiff but springy elements, such as fingered discs, spiders, or the like.

By the above means, release torque may be sufficiently closely controlled to achieve satisfactory operation of the mass produced sharpener even when it is employed as an attachment on powerful household appliances.

In connection with this aspect of the invention, it will be understood that the washers, although stiff, are not rigid. When this aspect of the invention is not involved, the washers may be rigid rather than springy.

Means are provided adjacent the periphery of each of the members 10 and 11 for restraining its associated abrasive Web 20 or 21 against the associated front face at the above-mentioned zone. These means comprise the am nular rims 36 and 37, each of which is telescopically engageable with the periphery of one of the members 10 and 11. Each of the rims 36 and 37 has a radially inwardly extending flange 38 or 39. The flanges 33 and 39 engage their associated abrasive web 20 or 21 and restrain it against the face of the associated member 10 The members 10 and 11 may be formed from a rubher or rubberlike composition or other elastomer. They should be hard enough to hold their shape without excessive spreading at operating speeds, for example, about 3200-3400 r.p.m., but they should be soft enough to conform to the knife blade with a good distribution of pressure. A durometer hardness of from 70-80 is preferred but the range 50-90 is acceptable. The support of flexible abrasive webs such as the webs 20 and 21 by elastomeric backing members, such as the members 10 and 11, which themselves are backed in their central portions by relatively stiff members, such as the washers 24 and 25, provides a sharpening structure having an annu lar guide groove which is capable of conforming to the blade during the sharpening operation but which Will not spread to allow the blade to penetrate deeply toward the central axis of the power shaft. Thus, the sharpening action is limited to the vicinity of the periphery of the annular sharpener to achieve an effective and superior sharpening action. Wholly satisfactory and relatively rapid sharpening may be readily accomplished even when the device is employed by inexperienced persons.

The above description of the invention should make it apparent that many details of the apparatus embodying the invention may be varied without departing from the teaching of the invention. Accordingly, the scope of the invention is not to be limited to precise details of the specifically described embodiment but is to be defined by the following claims.

What is claimed is:

1. A knife sharpener comprising a pair of annular elastomeric members mounted coaxially on a shaft, shoulder means on the shaft, each of said members having a front face in apposition to the other of said members, said front faces symmetrically curving relatively away from each other through a zone extending from radially intermediate locations to locations nearer the peripheries of said members, a pair of flexible abrasive webs each of which is supported against one of said front faces, said flexible abrasive webs being clamped by and between said members and against each other at locations radially inward of said zone, means adjacent the periphery of each of said members for restraining its associated abrasive web against the associated front face at said zone, each of said members having a rear face opposite to said front face, a stiff but springy washer received against each of said rear faces, each washer being radially inward of at least the majority of said zone, one of said washers engaging said shoulder means, the other of said washers being engaged by retaining means which is tightenable to a predetermined positively defined minimum axial distance along said shaft from said shoulder means such as to effect axial compression of both said washers.

2. A knife sharpener comprising a pair of annular elastomeric members mounted coaxially on a shaft, shoulder means on the shaft, each of said members having a front face in apposition to the other of said members, said front faces symmetrically curving relatively away from each other through a zone extending from radially intermediate locations to locations nearer the peripheries of said members, a pair of flexible abrasive webs each of which is supported against one of said front faces, said flexible abrasive webs being clamped by and between said members and against each other at locations radially inward of said zone, annular rims each telescopingly engageable with the periphery of one of said members, each rim having a radially inwardly extending flange, each flange engaging the associated abrasive web for restraining it against the associated front face at said zone, each of said members having a rear face opposite to said front face, a stiff but springy washer received against each of said rear faces, each washer being radially inward of at least the majority of said zone, one of said washers engaging said shoulder means, the other of said washers being engaged by retaining means which is tightenable to a predetermined positively defined minimum axial distance along said shaft from said shoulder means such as to effect axial compression of both of said washers.

3. A knife sharpener comprising a pair of annular elastomeric members mounted coaxially on a shaft, each of said members having a front face in apposition to the other of said members, said front faces symmetrically curving relatively away from each other through a zone extending from radially intermediate locations to locations nearer the peripheries of said members, a pair of flexible abrasive webs each of which is supported against one of said front faces, said flexible abrasive webs be ing clamped by and between said members and against each other at locations radially inward of said zone, annular rims each telescopingly engageable with the periphery of one of said members, each rim having a radially inwardly extending flange, each flange engaging the associated abrasive web for restraining it against the associated front face at said zone, each of said members having a rear face opposite to said front face, a stifi but springy washer received against each of said rear faces, each washer being radially inward of at least the majority of said zone, and clamping means on said shaft and engaging said washers, one of said washers engaging said shoulder means, the other of said washers being engaged by retaining means which is tightenable to a predetermined positively defined minimum axial distance along said shaft from said shoulder means such as to effect axial compression of both said Washers.

4. A knife sharpener comprising a pair of annular elastomeric members mounted coaxially on a shaft, each of said members having a front face in apposition to the other of said members, said front faces symmetrically curving relatively away from each other through a zone extending from radially intermediate locations to locations nearer the peripheries of said members, a pair of flexible abrasive webs each of which is supported against one of said front faces, said flexible abrasive webs being clamped between said members at locations radially inward of said zone, means adjacent the periphery of each majority of said zone, and clamping means on said shaft and engaging said stiff members.

5. A knife sharpener comprising a pair of annular elastomeric members mounted coaxially on a shaft, each of said members having a front face in apposition to the other of said members, said front faces symmetrically curving relatively away from each other through a zone extending from radially intermediate locations to locations nearer the peripheries of said members, a pair of flexible abrasive webs each of which is supported against one of said front faces, said flexible abrasive webs being clamped between said members at locations radially inward of said zone, each of said members having a rear face opposite to said front face, a stiff member received against each of said rear faces, each stiff member being radially inward of at least the majority of said zone, and clamping means on said shaft and engaging said stifi members.

References Cited in the file of this patent UNITED STATES PATENTS 48,755 Witsil July 11, 1865 248,020 Buzzell Oct. 11, 1881 440,948 Evans Nov. 18, 1890 1,675,223 McLaughlin June 26, 1928 2,798,345 Spear et a1. July 9, 1957 FOREIGN PATENTS 126,151 Switzerland June 1, 1928 487,743 Germany Feb. 25, 1928 

